[Lawrie]

tl:dr - check for a firmware update.

Long version:
I was getting this problem on my TabX with the older version 3.8.4x of MS AFTER a firmware update early in the year (January??).  I.E. the dark status bar with white print would go to white on white whenever I touched the bar and used the menu to change things like WiFi, Bluetooth, or frontlights.  Pretty much every time - it would eventually correct itself - I assume after some kind of re-write.  NB the Force refresh supplied by Boox did NOT fix this.  Nor was it limited to MS, I have another app which also does it.

Then, a few days ago (22nd of September?) I installed a new firmware update which I hoped would fix it, but it didn't.  

However, today's (for me) update to 3.9 has resolved the issue as far as I can see, with the change to black on white.  My only disappointment is that I actually preferred the white on black bar...  Oh well...